In response to the accident at Three Mile Island Unit 2, the federal government has required the development of symptom-related emergency operating procedures by utilities which operate nuclear power plants. The main objective of such procedures is to ensure that proper mitigating actions are implemented by licensed operators in the event of an accident. In addition, the criteria for implementing such mitigating actions identified in the emergency operating procedures must be based solely upon indications or symptoms observable by licensed operators using instrumentation within the control room of a nuclear station. The federal government has required the development and installation of instrumentation which can be used by operators in the control room to identify symptoms which are indicative of transient or accident conditions. Prior to the accident at Three Mile Island Unit 2, the typical response by an operator in a control room during a transient was to attempt to identify the event in progress and then to locate and implement a specific event mitigating procedure associated with the identified event. Since the accident at Three Mile Island Unit 2, the federal government has required utilities to develop emergency operating procedures which can by used by operators to mitigate emergency events independent of identification of their causes. The development of these symptom-related emergency operating procedures was intended to remove the possible errors an operator might make in trying to identify an event prior to attempting to mitigate it. Errors in event identification are possible by trained and licensed operators due to the vast numbers and combinations of possible indications which could appear on control room instrumentation due to different types of transients and accidents. The federal government and nuclear industry have acknowledged that the accident at Three Mile Island Unit 2 could have been mitigated had the operators utilized built-in plant features and responded to indications which identified a need for mitigating actions, rather than attempting to identify the event and to implement the proper mitigating procedures for the named event.
The means to classify emergency events so as to properly activate state and local governments has not in general improved in the same manner as emergency operating procedures since the accident at Three Mile Island Unit 2. Current federal regulations regarding event classification specify that four levels of emergency events be established and referenced in the emergency response plans for nuclear generating stations. Current federal guidance documents present general emergency class descriptions and detailed lists of example initiating conditions which were considered to be representative of each specific emergency class. As a result of following this guidance utilities have typically developed means to classify emergency events within nuclear power stations by requiring the licensed operator to identify the event in progress and to correlate the identified event to the listing associated with each emergency class presented in the federal guidance. This approach to emergency classification is currently employed by the majority of operating nuclear power stations and is consistent with federal requirements and guidance. This method of event classification requires the correct identification of the emergency event to ensure proper classification and to facilitate appropriate responses by state and local governments to ensure public protection. The result of this approach has been to introduce or maintain the existence of the same source of error, i.e., failure to properly identify the event, which was most significant in the accident at Three Mile Island Unit 2.